The present invention relates to an apparatus for cutting concrete columns and, particularly, is directed to such an apparatus for shortening prestressed concrete piles without severing the prestressing tendons therein.
Concrete piles of the type with which the present invention is intended to be used are typically precast with prestressing tendons formed therein and then driven into place at the construction site. Usually, the piles are of a length in excess of the ultimate length desired and, as a result, it is necessary to cut the piles to the desired length after they are driven into place.
One technique for cutting piles has been simply to saw the piles with an abrasive saw. This technique results in a relatively clean cut, but has the disadvantage that it severs the prestressing tendons in the pile, as well as the concrete. Severing the tendons is disadvantageous because it is generally desirable to leave the tendons extending from the free end of the pile in order that the tendons may be cast into the concrete slab or other structure ultimately to be supported on the piles. The sawing technique also has the disadvantage that it is relatively slow and that the saw blades require frequent replacement.
Another technique for cutting concrete piles has been simply to break the ends of the piles away with a jack hammer or similar device. This technique has the advantage that it preserves the tendons within the piles. It has the disadvantage, however, that it is very slow and expensive and results in a shortened pile wherein the distal end is of broken, irregular configuration.
The use of compression imparting techniques to divide or fracture stone or concrete is known in the prior art, as exemplified in U.S. Pat. Nos.: 247,569, 1,117,926; 3,062,294; and 3,705,747. U.S. Pat. Nos. 247,569 and 1,117,926 are concerned with devices to precisely split stones and U.S. Pat. No. 3,062,294 is concerned with an apparatus to fracture a subterranean formation. U.S. Pat. No. 3,705,747 is concerned with a demolition apparatus wherein crushing elements literally "chew" away the structure to be demolished. Although the structure disclosed in the latter patent bears some similarity to that of the present invention, it is no way suggests the apparatus of the invention which enables a column to be cut so as to leave a relatively planar end surface with the original column-reinforcing elements extending, intact, from the surface.
Additional prior art has been cited by the Patent Office during the prosecution of application Ser. No. 726,272 filed Sept. 24, 1976. The Valente U.S. Pat. No. 3,496,813 discloses an apparatus for shearing continuous billets which incorporates shears 96 and 98 which extend inwardly through the billet and actually cross each other during the shearing operation. In the present application, the shearing element is designed to perform two functions, i.e., first, the fracturing of the concrete column and, secondly, the crushing of a portion of the column above the shear plane. Valente makes no such suggestion.
Coffman U.S. Pat. No. 3,978,842 discloses a masonry block cutter which simply shears the masonry block, and is not designed to crush any portion of the block. Snell U.S. Pat. No. 82,886 shows a metal shear and does not suggest the crushing of the workpiece, let alone the breaking away of concrete from internal reinforcing tendons or reinforcing bars. Bowen U.S. Pat. No. 4,044,749 discloses a method and apparatus for breaking concrete from a concrete coated pipe to expose the pipe for repair work. Bowen uses three conical bits which are driven into the concrete and reciprocating through a 120.degree. arc to break the concrete away in chunks. Bowen does not teach a shear plane as does the present invention on one side of which it is desired to crush the concrete and below which it is desired not to break the concrete. The Sugiki U.S. Pat. No. 3,727,599 teaches a method for cutting hollow concrete piles, but does not suggest the combined shearing and crushing action above a designated shear plane as does the present invention. The McRee U.S. Pat. No. 3,056,267 discloses a pile cutter for severing submerged piles at the mud line. A blade passes through the pile, simply shearing the pile. No suggestion is made of a combined shear and crushing action as with the instant invention. The Kemble U.S. Pat. No. 1,366,693 teaches a shearing mechanism and again does not suggest the combined crushing and shearing action of the present invention.